The brain scans showed that several brain areas that were active while participants imagined themselves in the future were also active when they remembered themselves in the past.

But past and future didn't totally overlap in the brain. Some brain areas involved in picturing the future weren't as active in recalling the past.

For comparison, the researchers -- who included graduate student Karl Szpunar -- also asked participants to imagine former U.S. President Bill Clinton in specific settings, such as Clinton's past or future birthdays.

Why Clinton? Participants knew what he looks like but didn't know him personally.

Brain scans taken while participants thought about Clinton showed similar patterns of brain activity, but to a lesser extent, as when they thought about their own past and present.

"Our findings provide compelling support for the idea that memory and future thought are highly interrelated and help explain why future thought may be impossible without memories," Szpunar says in a university news release.

The findings may also help explain memory's role in evolution, Szpunar says.

"It may just be that the reason we can recollect our past in vivid detail is that this set of processes is important for being able to envision ourselves in future scenarios," he says.